Windows can only extend basic volumes into contiguous space after the existing volume.
You'll have to move the free space to be immediately after the volume you want to extend into it - which will require 3rd-party software.
My Computer
Computer type
Laptop
Computer Manufacturer/Model Number
Asus K52F or Lenovo B51-80
OS
Win 7 x64 Home Premium (and x86 VirtualBox VM)/Win10
CPU
i3 370M/i7 6500U
Motherboard
Asus/Lenovo
Memory
8GB - finally :)/8GB
Graphics Card(s)
it's an i3, dude!/dual Intel&nVidia
Sound Card
onboard
Monitor(s) Displays
15.6" built-in
Screen Resolution
1366x768/1920x1080
Hard Drives
750GB Seagate internal
Sundry external drives attached to other computers on the local network
1TB SSD on the Lenovo
PSU
n/a
Internet Speed
as much as I can get - usually on a dongle/phone, so <1MB/s